Indwelling heat exchange catheter and method of using same

ABSTRACT

A catheter is adapted to exchange heat with a body fluid, such as blood, flowing in a body conduit, such as a blood vessel. The catheter includes a shaft with a heat exchange region disposed at its distal end. This region may include hollow fibers which are adapted to receive a remotely cooled heat exchange fluid preferably flowing in a direction counter to that of the body fluid. The hollow fibers enhance the surface area of contact, as well as the mixing of both the heat exchange fluid and the body fluid. The catheter can be positioned to produce hypothermia in a selective area of the body or alternatively positioned to systemically cool the entire body system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/133,813 filed on Aug. 13, 1998, now U.S. Pat. No. 6,338,727 which isa continuation-in-part of U.S. patent application Ser. No. 09/063,984filed on Apr. 21, 1998, now issued as U.S. Pat. No. 6,126,684.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to apparatus and methods for producingheat exchange with body tissue, and more specifically to methods andapparatus for the hypothermic treatment of a body fluid in a bodyconduit.

2. Discussion of the Prior Art

Many of the advantages of hypothermia are well known. By way of example,it has been found particularly desirable to lower the temperature ofbody tissue in order to reduce the metabolism of the body. In stroke,trauma and several other pathological conditions, hypothermia alsoreduces the permeability of the blood/brain barrier. It inhibits releaseof damaging neurotransmitters and also inhibits calcium-mediatedeffects. Hypothermia inhibits brain edema and lowers intracranialpressure.

In the past, hypothermic treatment has been typically addressedsystemically, meaning that the overall temperature of the entire bodyhas been lowered to achieve the advantages noted above. This has beenparticularly desirable in surgical applications where the reducedmetabolism has made it possible to more easily accommodate lengthyoperative procedures. An example of this systemic approach includescatheters for transferring heat to or from blood flowing within apatient's vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. Aclosed loop heat exchange catheter is also disclosed by Saab in U.S.Pat. No. 5,624,392. A cooling device for whole-body hyperthermia thatutilizes the circulatory system of the body is known to be moreefficient since the entire volume of the body is constantly perfusedwith the cold fluid at a capillary level.

Likewise, various other means of cooling the body have been tried withcooling blankets, ice water bladder lavages, ice baths, esophagealcatheters and their associated methods. All of these devices require aconsiderable time to cool the body since the primary heat transferoccurs through the skin or the skull. A more efficient body coolingdevice that can quickly cool and accurately control the body temperatureis required.

SUMMARY OF THE INVENTION

A heat exchange catheter and method of operation are included in thepresent invention. The method is adapted to produce hypothermia orhyperthermia, typically in a selected portion of the body withoutsubstantially varying the temperature of the remaining portions of thebody. The selected body portion will usually be associated with a bodyconduit which conveys a body fluid to the selected body portion. Ofparticular interest are the organs of the body which are commonlynourished and maintained by a flow of blood in the arterial system. Forexample, a flow of blood is introduced to the brain through the carotidartery. Of course the temperature of this blood is usually at the normalbody temperature.

By positioning a heat exchange catheter in the body conduit, heat can beadded to or removed from the body fluid to heat or cool the selectedbody portion. For example, the heat exchange catheter can be disposed inthe carotid artery where the arterial blood flowing to the brain can becooled. The flow of cooled blood to the brain reduces the temperature ofthe brain thereby resulting in cerebral hypothermia. Importantly, thistemperature reduction occurs primarily and selectively in the brain; theremaining portions of the body maintain a generally normal bodytemperature. In accordance with this method, the selected body portion,such as the brain, can be cooled thereby providing the advantagesassociated with hypothermia for this body portion. The remainder of thebody, such as the portions other than the brain, do not experience thereduction in temperature. Furthermore, the invention is intended toremotely alter temperature in a region other than the point ofintroduction into the body. This is different than devices intended forsystemic temperature control.

Several factors are of interest in effecting heat transfer in a heatexchanger. These factors include, for example, the convection heattransfer coefficient of the two fluids involved in the heat exchange, aswell as the thermal conductivity and thickness of the barrier betweenthe two fluids. Other factors include the relative temperaturedifferential between the fluids, as well as the contact area andresidence time of heat transfer. The Reynolds number for each fluidstream affects boundary layers, turbulence and laminar flow.

Notwithstanding the need for localized hypothermia, there will always bethose procedures which call for systemic hypothermia. Many of theadvantages associated with the present invention will greatly facilitatethose procedures, for example, by decreasing the number and complexityof operative steps, increasing the heat transfer capacity of the device,and addressing other concerns such as the formation of blood clots.

In one aspect of the invention a catheter is provided with an elongateconfiguration, a proximal end and a distal end. An outer tube having afirst lumen extends between the distal end and proximal end of thecatheter, and an inner tube having a second lumen is disposed within thefirst lumen of the outer tube. Portions of the inner tube define a firstflow path extending along the second lumen, while portions of the tubesdefine a second flow path extending between the first tube and thesecond tube. A plurality of hollow fibers provide fluid communicationbetween the first and second flow paths, and a heat exchange fluid isdisposed in the hollow fibers to cool the fibers.

In another aspect of the invention, a method for making a heat exchangecatheter includes the steps of providing first and second tubes havingfirst and second lumens, respectively. A plurality of hollow fibers areconnected between a first flow path extending along the second lumen anda second flow path extending along the first lumen outwardly of thesecond tube. The method further comprises the step of insuring that thesecond tube is axially or rotationally movable relative to the firsttube in order to vary the configuration of the hollow fibers.

In a further aspect of the invention, a method for operating a heatexchange catheter includes the steps of inserting into a body conduitthe catheter with an inner tube disposed within an outer tube anddefining a first flow path interiorly of the inner tube and second flowpath between the inner tube and the outer tube. This inserted catheteralso includes a plurality of hollow fibers disposed in fluidcommunication with the first and second flow paths. The method furtherincludes steps for creating a flow of heat exchange fluid through thefirst and second flow paths, and moving the inner tube relative to theouter tube to change the profile of the hollow fibers.

In a further aspect of the invention, a heat exchange catheter includesan elongate shaft with first portions defining an inlet lumen and secondportions defining an outlet lumen. A first manifold is disposed in fluidcommunication with the inlet lumen and a second manifold disposed influid communication with the outlet lumen. A plurality of hollow fibersare disposed between the manifolds in fluid communication with the inletand outlet lumens. The catheter is adapted to receive a heat exchangefluid and to direct the heat exchange fluid through the hollow fibers toexchange heat through the hollow fibers.

In still a further aspect of the invention, a catheter is adapted toexchange heat with the body fluid flowing in a first direction through abody conduit. The catheter includes a shaft having an input lumen and anoutput lumen. A plurality of hollow fibers define a heat exchange regionand collectively define an output surface of the heat exchange region.The input lumen of the shaft is coupled to the hollow fibers at a firstlocation while the output lumen of the shaft is coupled to the hollowfibers at a second location disposed in the first direction from thefirst location.

Another aspect of the invention includes a method for exchanging heatwith a body fluid in a body conduit. In this case, a catheter isprovided with a plurality of hollow heat exchange fibers extending influid communication with an inlet lumen and an outlet lumen of thecatheter. The heat exchange fibers collectively define a first cavity inheat transfer relationship with a body fluid in a body conduit.

In an additional aspect of the invention, an operative area of thecatheter is sized and configured for disposition in a vessel containingblood. The operative area is adapted to perform a predeterminedfunction, and the blood in the vessel has a tendency to form clots. Inthis aspect of the invention, the catheter is provided with a snaredisposed relative to the operative area and being operable from aproximal end of the catheter to move from a low-profile statefacilitating insertion of the catheter, to a high-profile statefacilitating the capture of blood clots.

In still a further aspect of the invention, a heat exchange catheter isadapted for cooling the blood of a patient. The catheter includes a heatexchange region with a plurality of fibers each having a hollowconfiguration. A heat exchange fluid is disposed in the hollow fibers tocool the fibers and a coating is disposed on the outer surface of thefibers to inhibit formation of blood clots.

These and other features and advantages of the invention will be betterunderstood with a description of the preferred embodiments of theinvention and reference to the associated drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is side elevation view of a patient lying in a prone positionwith a heat exchange catheter of the present invention appropriatelyinserted to facilitate hypothermic treatment of the patient's brain;

FIG. 2 is an enlarged side elevation view showing the vasculatureassociated with the patient's head and brain;

FIG. 3 is a perspective view partially in section of a heat exchangeregion of the catheter;

FIG. 4 is an enlarged axial cross section view of a plurality ofballoons disposed in the heat exchange region of the catheter;

FIG. 5 is a radial cross section view of the catheter taken along lines5—5 of FIG. 4;

FIG. 6 is a radial cross section view similar to FIG. 5 of a furtherembodiment of the catheter;

FIG. 7 is a perspective view of a further embodiment of the catheterwherein multiple balloons are provided with a longitudinalconfiguration;

FIG. 8 is a radial cross section view taken along lines 8—8 of FIG. 7;

FIG. 9 is an axial cross section view taken along lines 9—9 of FIG. 7;

FIG. 10 is a perspective view of the catheter illustrated in FIG. 3further illustrating structures which can facilitate mixing and heatexchange;

FIG. 10A is a perspective view of an embodiment of the catheter having adistal end with a pigtail configuration;

FIG. 10B is a perspective view of the catheter illustrated in FIG. 10Awith the distal end straightened by a stylet 174 to facilitate insertionof the catheter;

FIG. 11 is a schematic view of an embodiment including a heat pipe;

FIG. 12 is a schematic view, partially in section, of a heat pipeadapted for use in the embodiment of FIG. 11;

FIG. 13 is a top plan view of carotid artery branch illustrating onemethod of operation associated with the catheter;

FIG. 14 is a top plan view similar to FIG. 13 and showing a furthermethod of operation with the catheter;

FIG. 15 is a top plan view of the carotid branch similar to FIG. 13 andshowing a further method of operating a heat exchange catheter;

FIG. 16 is a radial cross section of the catheter taken along lines16—16 of FIG. 15;

FIG. 17 is an axial cross section view of a further embodiment of theinvention including hollow fibers in the heat exchange region;

FIG. 18 is a side elevation view similar to FIG. 17 and illustrating thehollow fibers in a compacted configuration; and

FIG. 19 is an axial cross section view of the catheter of FIG. 17operatively disposed and configured to permit the hollow fibers to floatand undulate within a blood stream.

FIG. 20 is a side elevation view partially in section and illustrating afurther embodiment of the catheter of the present invention;

FIG. 21 is a radial cross-section view taken along the lines 21—21 ofFIG. 20;

FIG. 22 is an axial cross-section view of the proximal end of thecatheter illustrated in FIG. 20;

FIG. 23 is an axial cross-section view of the distal end of a furtherembodiment illustrating the heat exchange region in a low-profile state;

FIG. 24 is an axial cross-section view similar to FIG. 23 andillustrating the heat exchange region in a high-profile state;

FIGS. 25-27 illustrate a preferred method for manufacturing the heatexchange region of a hollow fiber embodiment of the cavity;

FIG. 25 is a top plan view of a mat formed of the heat exchange fibers;

FIG. 26 is a perspective view illustrating formation of the mat aroundthe distal ends of the concentric tubes;

FIG. 27 is a side elevation view illustrating attachment of the matassembly to an outer tube of the catheter;

FIG. 28 is a top-plan view of a patient illustrating portions of theblood circulatory system;

FIGS. 29-33 illustrate a method for introducing the catheter of thepresent invention;

FIG. 29 is a side elevation view illustrating a introducing sheath in afirst position removed from the heat exchange region;

FIG. 30 is a side elevation view illustrating the sheath in a secondposition over the heat exchange region of the catheter;

FIG. 31 is a side elevation view illustrating the catheter and sheathbeing inserted into an introducer;

FIG. 32 is a side elevation view illustrating the catheter furtherinserted with the sheath maintained in the introducer;

FIG. 33 is a side elevation view illustrating removal of the sheath tothe first position;

FIG. 34 is a perspective view of a further embodiment of the catheterincluding a distal clot filter in a low-profile state;

FIG. 35 is a perspective view illustrating the catheter of FIG. 34 withthe clot filter in a high-profile state;

FIG. 36 is a perspective view of a catheter with a clot filter havingfree ends and automatically deployable to a high-profile state; and

FIG. 37 is a side elevation view of the catheter of FIG. 36 with asheath maintaining the clot filter in a low-profile state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE OF THE INVENTION

A heat exchange catheter is illustrated in FIG. 1 and designatedgenerally by the reference numeral 10. The catheter 10 is operativelydisposed with respect to a body 12 of a patient having a groin 14, ahead 16, and a brain 18. More specifically, the catheter 10 can beinserted percutaneously through a puncture or surgical cut down at thegroin 14, and into the femoral artery 21. Following this initialintroduction, the catheter 10 can be moved through the femoral artery 21and the aortic arch 23, into the common carotid artery 25 bestillustrated in FIG. 2. This common carotid artery 25 divides at acarotid branch 27 into an external carotid artery 30, which primarilysupplies blood 1 to the face of the patient, and an internal carotidartery 32, which primarily supplies blood to the brain 18 of thepatient.

In the concept of this invention, the brain 18 is merely representativeof a portion of the body 12 of the patient, and the arteries 21, 25, 30and 32 are merely representative of conduits which supply a body fluid,such as blood, to a selected portion of the body 12, such as the brain18. By cooling the body fluid, such as blood 31, in the body conduit,such as the artery 32, the specific body portion, such as the brain 18,can be selectively cooled without significantly affecting thetemperature of the remaining portions of the body 12.

Selective hypothermic treatment of the brain 18 is initially ofparticular interest as it captures the advantages of hypothermia duringoperative procedures associated with the brain 18 without also capturingthe disadvantages of hypothermia with respect to other areas of the body12. Thus, a surgeon operating to treat an aneurysm in the brain 18, forexample, can initially cool the brain 18 in order to facilitate thatprocedure. This selective hypothermia will be particularly appreciatedin those surgical procedures which are primarily directed to the brain18. Procedures such as stroke, trauma, and other brain related injurieswill also benefit up to and during from this selective hypothermiatreatment.

A preferred embodiment of the catheter 10 of the present invention isillustrated in FIGS. 3 and 4. From this perspective view, it can be seenthat the catheter 10 includes a shaft 40 having an axis 41 which extendsbetween a proximal end 43 and a distal end 45. When operativelydisposed, a heat exchange region 47 at the distal end 45 is operativelydisposed within the body 12, and a hub 50 at the proximal end 43 isdisposed outside of the body 12. Within the shaft 40, a plurality oflumens 52 and 54 extend in fluid communication with the hub 50 and theheat exchange region 47.

A preferred embodiment of the heat exchange region 47 is illustrated ingreater detail in FIG. 4 where three balloons 56, 58 and 61 areindividually, separately and axially disposed along the shaft 40. Itwill be appreciated that although the illustrated embodiment includesthree balloons, a single balloon or double balloon embodiment may offerfurther advantages in a particular procedure. All of the balloons 56, 58and 61 are illustrated to have a significantly larger diameter than theshaft 40. This may not be the case in other embodiments. Morespecifically, it may be desirable to maximize the dimension of the shaft40 in order to facilitate flow of the heat exchange fluid. This willalso minimize the volume of fluid in the balloon and promote a morerapid heat exchange. In one such embodiment, the diameter of the shaft40 is in a range between 50 and 90 percent of the diameter of theballoons 56, 58 and 61.

Each of the balloons 56, 58 and 61 can be formed from a piece of sheetmaterial 62, 64 and 66 which is bound or otherwise fixed to the shaft 40to form a cavity 63, 65 and 67, respectively. An inlet hole 70 providesfluid communication between the lumen 54 and the cavity 63 of theballoon 56. Similar inlet holes 72 and 74 are provided for the balloons58 and 61. In a like manner, an outlet hole 76 can be formed in the wallof the shaft 40 to provide fluid communication between the lumen 52 andthe cavity 63 of the balloon 56. Similar outlet holes 78 and 81 areprovided for the balloons 58 and 61, respectively. With this structure,it can be seen that the lumen 54 functions primarily as an inlet lumenfor a heat exchange fluid which is illustrated generally as a series ofarrows designated by the reference numeral 85.

Initially, the heat exchange fluid 85 is introduced through the hub 50(FIG. 3) and into the inlet lumen 54. From the lumen 54, the heatexchange fluid 85 passes through the inlet holes 70, 72, 74 and into therespective balloon cavity 63, 65 and 67. The heat exchange fluid 85 thenpasses into the outlet hole 76, 78, 81 and into the outlet lumen 52 andthe hub 50 to regions exterior of the catheter 10.

After the heat exchange fluid 85 is remotely cooled, it is circulatedthrough the balloon cavities 63, 65 and 67 to provide a cold temperaturefluid on the inner surface of the sheet materials 62, 64 and 66 whichform the walls of the balloons 56, 58 and 61, respectively. With a bodyfluid, such as blood 31, flowing exteriorly of the balloons 56, 68 and61, heat transfer occurs across the sheet materials 62, 64 and 66,respectively.

It can be appreciated that this circulation of the heat exchange fluid85 can be formed with any structure of the shaft 40 which provides twolumens, such as the lumens 52 and 54, each of which can have access tothe balloon cavities, such as the cavities 63, 65 and 67. In oneembodiment of the shaft 40 illustrated in FIG. 5, a septum 90 isprovided which separates the cylindrical shaft 40 into two equally sizedlumens 52 and 54. In the embodiment of FIG. 6, the cylindrical shaft 40is provided with a cylindrical septum 92 which provides the lumen 54with a circular cross section and the lumen 52 with a moon-shaped crosssection. In such an embodiment, the lumen 54 must be defined off-axisfrom the shaft 40 in order to have access to the balloon cavities, suchas the cavity 63.

One of the advantages of a multiple balloon embodiment of the catheter10 is that the flow and temperature of the heat exchange fluid 85 can bemore easily controlled along the entire length of the heat exchangeregion 47. Realizing that the heat exchange fluid 85 will be coolestprior to entering into a heat exchange with the blood 31, and warmestafter that heat exchange, one can advantageously control not only thevelocity and volume of flow, but also the direction of flow within eachdiscrete balloons 56, 58 and 61. Another advantage of a multiple balloondesign is the ability of the catheter to bend and flex when placed in acurved vasculature. Single balloon designs would be rigid, stiff andinflexible by comparison.

In order to facilitate the maximum heat exchange between the fluid 85and the blood, it is desirable to provide a balanced flow of the heatexchange fluid 85 along the entire length of the heat exchange region47. In the embodiment illustrated in FIG. 4, efficient heat transfer isfacilitated by countercurrent flow where the heat exchange fluid 85 isdirected to flow counter to the flow of the blood 31. To that end, theinlet holes 70, 72 and 74 are positioned distally of the outlet holes76, 78 and 81, respectively. As the blood 31 flows distally along theouter surface of the catheter 10, this relative position of the inletholes and outlet holes causes the heat exchange fluid to flow in theopposite direction, proximally in each of the balloons 56, 58 and 61.

The amount of flow within each of the balloons 56, 58 and 61 can also becontrolled by the size of the inlet holes 70, 72, 74 and outlet holes76, 78 and 81. In a preferred embodiment, this flow control is providedsolely by the inlet holes 70, 72 and 74; the outlet holes 76, 78 and 81are sized larger than their respective inlet holes so that they offerlittle resistance to flow. In this embodiment, the inlet holes 70, 72and 74 are sized to be progressively smaller from the distal end 45 tothe proximal end 43. Thus the hole 70 is larger than the hole 72 whichis larger than the hole 74. As a result, the resistance to the flow ofheat exchange fluid 85 in the most distal balloon 56 is less than thatin the most proximal balloon 61. This ensures that the coolest heatexchange fluid 85 is shared equally among all of the balloons 56, 58 and61 regardless of their position along the shaft 40. In an embodimentwherein the flow is controlled by the outlet holes 76, 78 and 81, theseholes can also be provided with a relatively reduced size from thedistal end 45 to the proximal end 43. With any of these structures, amore balanced flow of the heat exchange fluid can be achieved in orderto facilitate the highest degree of heat exchange along the entire heatexchange region 47. Alternatively, the flow of heat exchange fluid canalso be balanced by providing the holes 76, 78 and 81 with non-circularconfigurations. For example, these holes may be formed as longitudinalslits extending axially of the catheter.

A further embodiment of the invention is illustrated in FIG. 7 wherein asingle sheet of material 101 is used to form separate and distinctindividual balloons, two of which are designated by the referencenumerals 103 and 105. As opposed to the radial balloons 56, 58 and 61 ofthe previous embodiment, the balloons 103 and 105 extend axially alongthe surface of the shaft 40. For example, the balloons 103 and 105 formindividual balloon cavities 107 and 110, respectively, which extend froma distal end 112 to a proximal end 114.

This embodiment of the catheter containing the axial balloons 103 and105 may include a shaft 40 with a slightly different configuration. Asbest illustrated in FIG. 9, the shaft 40 may include an outer tube 121having an outer surface to which the sheet material 101 is attached andwithin which is disposed a distal sealing plug 123. An inner tube 125,which can be disposed coaxially with the outer tube 121, has an innerlumen 127 and defines with the outer tube 121 an outer lumen 130. A pairof inlet holes 132 and 134 provide flow fluid communication between theinner lumen 127 and the balloon cavities 107 and 110, respectively.Similarly, a pair of outlet holes 136 and 138 provide fluidcommunication between the balloon cavities 107 and 110 and the outerlumen 130, respectively. An inner plug 141 disposed between the innertube 125 and outer tube 121 to seal the outer lumen 130 between theinlet holes 132, 134 and outlet holes 136, 138. For the reasonspreviously noted, a preferred embodiment has inlet holes 132, 134 whichare disposed distally of and sized smaller than the outlet holes 136,138, respectively. This orientation will provide countercurrent flow ina catheter 10 which is inserted downstream into an artery such as thecarotid artery 25.

Embodiments which are intended to maximize heat transfer will takeadvantage of the fact that heat exchange is enhanced when either, orboth, the body fluid or the heat exchange fluid is provided with wellmixed flow. Mixing can be enhanced by providing irregular surfaces nextto which either of these fluids flow. For example, with reference toFIG. 4, it will be noted that a spring 150 can be disposed around theshaft 40 inside each of the balloons, such as the balloon 61. In thisembodiment, the spring 150 upsets the laminar flow of the heat exchangefluid 85 thereby producing the desired mixing of this fluid. Otherstructures can be positioned within the cavities formed by the balloons56, 58 and 61.

Mixing can also be enhanced within the body fluid which flows along theouter surface of the catheter 10. In this case, the multiple radialballoon embodiment illustrated in FIG. 4 is of advantage as each of theballoons 56, 58 and 61 represents a peak and defines with the adjacentballoon a valley along which the blood 31 flows. This series of peaksand valleys also upsets the laminar flow of the body fluid. Mixing ofthe body fluid can also be enhanced by providing other structures alongthe outer surface of the sheet material 62, 64 and 66 which form theballoons as well as any exposed areas of the shaft 40 in the heatexchange region 47. By way of example, a multiplicity of granules 145can be adhered to the outer surface of the radial balloons 56, 58 and 61or the axial balloons 103 and 105 as illustrated in FIG. 9. Ridges canalso be provided along these surfaces.

With some body fluids, it may be desirable to inhibit turbulent flow andfacilitate laminar flow. This may be true for example in the case ofblood where undesirable hemolysis may occur in response to increasedturbulence. Such an embodiment might be particularly desirable for usewith radial balloons where an outer balloon 152 would promote laminarflow by reducing the height differential between the peaks and valleysdefined by the balloons 56, 58 and 61. This outer balloon 152 is bestillustrated in FIG. 10. To further promote laminar flow, the outersurface of any structure in the heat exchange region 47 can be providedwith a coating 154, such as a hydrophilic or a hydrophobic coating tomodify the boundary layer. Thus the outer surface of the shaft 40 aswell as the outer surface of any of the balloons 56, 58, 61, 103, 105and 152 can be provided with the coating 154. The coating 154 may alsoinclude other ingredients providing the catheter 10 with additionaladvantageous properties. For example, the coating 154 may include anantithrombogenic ingredient such as heparin or aspirin. Such a coating154 would not only inhibit platelet deposition but also the formation ofblood clots.

As previously noted, the characteristics of the heat exchange fluid 85may also be of importance in a particular heat exchange environment.Although the heat exchange fluid 85 may include various liquids, it isbelieved that gases may provide the greatest temperature differentialwith the body fluid. Particularly if this fluid includes blood, gasesthat are inert or otherwise compatible with the vascular system will beappreciated. Although several inert gases might fulfill theserequirements, carbon dioxide is used for the heat exchange fluid 85 in apreferred embodiment of the invention.

A further embodiment of the catheter 10 is contemplated for maximizingthe surface area available for heat exchange. As illustrated in FIGS.10A and 10B, the catheter 10 can be formed with a distal end 45 of theshaft 40 disposed in the natural configuration of a spiral or pigtail172. The relatively large diameter of the pigtail 172 facilitates heatexchange, but tends to deter from a low profile desire for insertion.Under these circumstances, it may be advantageous to insert the catheter10 over a stylet or guidewire 174 in order to straighten the pigtail 172as illustrated in FIG. 10B.

Hyperthermia and hypothermia for selective regions of the body can alsobe achieved by placing in the body conduit, such as the carotid artery25, a heat pipe 161 best illustrated in the schematic view of FIG. 11.In this embodiment, the heat pipe 161 includes a distal end 163 andproximal end 165. The distal end 163 is adapted to be placed within thebody conduit, such as the carotid artery 25. The proximal end 165 of theheat pipe 161 is adapted to be connected to an external heat sink orcooler, such as a thermoelectric cooler 167 or water jacket 168. A wickstructure 170 is provided in the heat pipe 161 to facilitate a flow ofheat exchange fluid from the cooler 167 to the distal end 163.

In a process involving the heat pipe 161, illustrated in FIG. 12, theheat exchange fluid is moved from the proximal end 165 of the heat pipe161 either by gravity or by capillary action of the wick structure 170to the distal end 163. At the distal end 163 of the heat pipe 161, heatis transferred from the body fluid, such as blood, to the heat exchangefluid in its liquid state. This heat exchange liquid absorbs a heat ofvaporization as it passes into a vapor state in the heat pipe 161. Theheat exchange fluid in its vapor state creates a pressure gradientbetween the ends 163 and 165 of the heat pipe 161. This pressuregradient causes the vapor to flow to the cooler 165 where it iscondensed giving up its latent heat of vaporization. The heat exchangefluid in its liquid state then passes back through the heat pipe 161through the wick structure 170 or by gravity. The passive heat exchangesystem provided by the heat pipe 161 is vacuum-tight and can be operatedwith a minimum amount of the heat exchange fluid.

Although the heat exchange catheter 10 will be advantageous in thehyperthermic or hypothermic treatment of any portion of the body 12, itis believed that it will be particularly appreciated in those procedureswhich can benefit from the hypothermic treatment of the brain 18, suchas the treatment of ischemic stroke and/or head trauma. As previouslynoted in comments directed to FIG. 1, the catheter 10 can be insertedinto the femoral artery in the groin 14 and directed through the aorticarch 23 into the common carotid artery 25. As illustrated in FIG. 13,the catheter 10 can then be moved into the region of the arterial branch27 where it will encounter the external carotid artery 30 and theinternal carotid artery 32. Since the external carotid artery 30 isdirected primarily to the facial regions, it does not supply asignificant amount of blood to the brain 18. In contrast, the internalcarotid artery 32 is almost solely responsible for feeding the capillarybed of the brain 18. Based on these considerations, hypothermictreatment of the brain 18 is best addressed by cooling the blood in theinternal carotid artery 32 without wasting any of the cooling propertieson the external carotid artery 30. In a method associated with oneembodiment of the invention, the most distal of the balloons, such asthe balloon 56 in FIG. 13 is preferably positioned within the internalcarotid artery 32. The more proximal balloons 58 and 61 can be disposedalong the common carotid artery 25. This embodiment of the catheter 10and its associated method will achieve a higher degree of heat transferwithin the internal artery 32 than the external artery 30.

In another embodiment of the catheter 10 best illustrated in FIG. 14, anocclusion balloon 175 is provided distally of the heat exchange region47. In this embodiment, the occlusion balloon 175 will preferably beinflatable through a separate lumen in the shaft 40. As the catheter 10,approaches the carotid branch 27, the occlusion balloon 81 is directedinto the external carotid artery 30 and inflated in order to at leastpartially occlude that artery. The remaining proximal balloons 56, 58and 61 in the heat exchange region 47 are left within the common carotidartery 25 to promote heat exchange with the blood flowing to the branch27. With the external artery 30 at least partially occluded, heattransfer occurs primarily with the blood flowing into the internalcarotid artery 32.

A further embodiment of the invention is illustrated in FIG. 15operatively disposed in the common carotid artery 25 and internalcarotid artery 32. In this case, the catheter 10 includes a balloon 181which is attached to the distal end of the shaft 40 and provided with aspiral configuration. More specifically, the balloon 181 may be formedfrom several individual balloons, as with the embodiment of FIG. 7, foras individual flutes 183 on the single balloon 181. In either case, theseparate balloons (such as the balloons 103, 105 of FIG. 7) or theflutes 183 are oriented in a spiral configuration around the axis 41 ofthe catheter 10. The shaft 40 can be provided with any of theconfigurations previously discussed such as the eccentric configurationof FIG. 6.

By providing the balloon 181 with a spiral configuration, heat exchangeis enhanced by at least two of the factors previously discussed.Notably, the surface area of contact is increased between the blood 31flowing externally of the balloon 181 and the heat exchange fluidflowing internally of the balloon 181. The spiral configuration alsoenhances the mixing properties of both the blood 31 and the heatexchange fluid 85.

As noted, the heat exchange fluid 85 may be cooled to a sub-zerotemperature. In order to thermally protect the internal lining of theartery 32 from direct contact with the subzero coolant, it may bedesirable to provide the tips of the flutes 183 with a thicker wall 185,as shown in FIG. 16. This thicker wall 185 might be advantageous in anyof the balloon configurations previously discussed, but would appear tobe most advantageous in the embodiments of FIGS. 7 and 15 where thecontact with the artery 32 tends to be more localized by thelongitudinal balloons 103, 105 (FIG. 7) on the spiral flutes 183 (FIG.15).

Still a further embodiment of the invention is illustrated in FIG. 17.In this embodiment, the shaft 40 includes an inner tube 190 disposedwithin an outer tube 192. These tubes 190, 192 may be concentric andlongitudingly movable relative to each other. The tubes 190, 192terminate respectively in manifolds 194, 196. Between these manifolds194, 196, a multiplicity of hollow fibers 198 can be disposed at thedistal end 45 to define the heat exchange region 47 of the catheter 10.The hollow fibers 198 each include an internal lumen which providesfluid communication between the manifolds 194 and 196. In operation, theheat exchange fluid 85 flows distally along the inner tube 190 into thedistal manifold 194. From this manifold 194, the heat exchange fluid 85flows into the internal lumens of the hollow fibers 198 proximally tothe proximal manifold 196. The warmer heat exchange fluid 85 flowsproximally from the manifold 196 between the inner tube 190 and outertube 192.

Preferably, the hollow fibers 198 have a wall thickness that is thinenough to allow maximum heat transfer, yet strong enough to withstandthe pressure requirements of the heat exchange fluid 85. The hollowfibers 198 are further adapted to achieve ideal heat transfer by themaximization of both surface area and coolant flow. The smaller thediameter of the fibers 198, the more fibers can be fit into the catheter10 with a corresponding increase in surface area. As the diameter of thefibers 198 is decreased, however, the resistance to fluid flow increasesthus lowering the coolant flow rate. The effect of the inflow andoutflow lumens must also be considered in determining the fluidresistance. Ideally, the wall thickness of the hollow fibers 198 is in arange between 0.00025 inches and 0.003 inches. In a preferred embodimentthe wall thickness is in a range between 0.00075 inches and 0.002inches, and ideally 0.00125 inches. The outer diameter of the hollowfibers 198 will typically be between 0.008 inches and 0.035 inches. In apreferred embodiment the outer diameter is in a range between 0.010inches and 0.018 inches, and ideally 0.015 inches.

It will be noted that the heat exchange fluid 85 flowing in the innertube 190 is insulated in several respects from the blood stream outsidethe catheter 10. This flow channel in the inner tube 190 is insulatednot only by the wall of the outer tube 192, but also by the coolantreturning in the flow channel associated with the outer tube 192. Theheat exchange fluid 85 in the inner tube is further insulated by thethickness of the inner tube wall.

In the heat exchange region 47, the wall thicknesses associated with theinner tube 190 and the outer tube 192 is preferably reduced in order toprovide additional volume for the hollow fibers 198. With a reduced wallthickness, the inner tube 190 also contributes to the heat exchangeoccurring in the region 47.

The hollow fibers 198 offer several advantages to this embodiment of thecatheter 10. Notably, they provide a very high surface area between theblood 31 and the heat exchange fluid 85. This greatly enhances the heatexchange characteristics of this embodiment. Countercurrent flow canalso be maintained further facilitating the heat exchange capabilitiesof this catheter.

The hollow fibers 198 can be spiraled as illustrated in FIG. 18 bytwisting the inner tube 190 with respect to the outer tube 192. Thischaracteristic can be used to provide a shorter and lower profile heatexchange region 47 in order to facilitate introduction of the catheter10. A lower profile may also be obtained by separating the manifolds 194and 196 a distance substantially equal to the length of the fibers 198.This will tend to hold the fibers in a straight, parallel relationshipand thereby facilitate introduction of the catheter 10. The spiraledconfiguration of the hollow fibers 198 can be maintained during heatexchange in order to further increase the heat exchange area per unitlength of the catheter 10. Alternatively, the fibers 198 can bepositioned to loosely float and undulate between the manifolds 194 and196 as illustrated in FIG. 19. This characteristic of the fibers 198will not only provide the increased heat exchange area desired, but alsopromote mixing within the blood 31.

The fibers 198 will typically be formed of common materials such aspolyolefin nylon and polyurethane. The fibers can be coated with aclot-inhibiting material such as heparin. Other materials advantageousfor inhibiting the formation of blood clots might include those whichform polymer surfaces with 16 or 18 carbon alkyl chains. These materialsattract albumin and thereby inhibit clot formation. In a furtherembodiment, the fibers 198 can be provided with micropores which permitthe leaching of such clot inhibiting pharmaceuticals as heparinizedsaline which could also serve as the heat exchange fluid 85.

The embodiment of FIG. 20 also takes advantage of the significant heatexchange characteristics associated with the hollow fibers 198. In thisembodiment, the manifold 194 at the distal end 45 of the catheter 10includes a potting seal 201 with a distal surface 203. The fibers 198are held in the potting seal 201 with the lumens of the fibers 198exposed at the surface 203. The distal end of the inner tube 190 is alsoheld in the potting seal 201 with its lumen exposed at the distalsurface 203. In this embodiment, the manifold 194 includes a cap 205which may have a hemisphere configuration. This cap extends over thedistal surface 203 of the potting seal 201 and provides fluidcommunication between the lumen of the inner tube 190 and the lumens ofthe hollow fibers 198. This cap 205 may also be constructed of materialsand wall thicknesses that insulate the blood vessels from potentialcontact with a cold catheter tip.

FIG. 21 illustrates in a cross-sectional view a first flow channel 204which extends along the lumen of the inner tube 190 and a second flowchannel 206 which extends along the lumen of the outer tube 192outwardly of the inner tube 190. As the heat exchange fluid 85 isintroduced into the first flow channel 204, its direction is reversed incap 205 so that the flow of the fluid 85 in the hollow fibers is counterto the flow of the body fluid, such as blood, in the body conduit, suchas the artery 32. After moving through the fibers 198, the heat exchangefluid 85 passes along the second flow channel 206 between the inner tube190 and outer tube 192, and exits the catheter 10 at the proximal end43.

The embodiment of FIG. 20 also includes a Y-connector 207 disposed atthe proximal end 43 of the catheter 10. This connector 207 is shown ingreater detail in the enlarged view of FIG. 22. In this view it can beseen that the connector 207 includes a body 210 with screw threads 212at its distal end and screw threads 214 at its proximal end. At thedistal end of the body 210, a screw cap 216 mates with the screw threads212 to engage an annular flange 218 at the proximal end of the outertube 192. In this manner, the Y-connector 207 forms a seal with theproximal end of the outer tube 192 and provides fluid communicationbetween the second flow channel 206 and a lumen 221 of the Y-connector207. A side port 223 communicates with this lumen 221 and provides anexit port for the secondary flow channel 206.

In order to prevent leakage from the lumen 221 at the proximal end 43 ofthe Y-connector 207, a releasable seal 225 can be formed at the proximalend of the body 210. In the illustrated embodiment, the releasable seal225 includes a cap 227 which is threaded to register with the threads214 of the body 210. This cap 227 extends around the proximal end of thebody 210 and compresses an elastomeric washer 230 against the body 210and the outer surface of the inner tube 190. By tightening the cap 227,the washer 230 is compressed to seal the lumen 221. This compressionalso functions to inhibit, but not necessarily prevent, axial movementbetween the outer tube 192 and inner tube 190. The releasability of theseal 225 can be appreciated in order to facilitate this relativemovement between the tubes 190 and 192 for the reasons previouslydiscussed. This form of a releasable-seal 225 is commonly referred to asa Tuohy-Borst seal.

The relative movement between the inner and outer tubes 190 and 192,respectively, will be appreciated in order to provide the tubes 190 and192 with a first position wherein the fibers 198 have a low profileconfiguration as illustrated in FIG. 23. The relative movement will alsobe appreciated in order to provide the tubes 190 and 192 with a secondposition wherein the hollow fibers 198 form an increased profile asillustrated in FIG. 24. It can be appreciated that this profile willfacilitate heat exchange by providing an increased spacing of theindividual hollow fibers in the body fluid.

Another feature associated with these two positions is illustrated inFIG. 23 where the inner tube 190 is expanded in thickness at its distalend in order to form a ramp or taper 232. In this embodiment, the taper232 is annular and extends radially outward with progressive distalpositions along the tube 190. As the inner tube 190 is drawn proximallyrelative to the outer tube 192, the taper 232 is brought into sealingengagement with the proximal end of the hollow fibers 198 and pottingseal 201. This effectively seals the distal end of the outer tube 192against the outer surface of inner tube 190, and prohibits any loss ofthe heat exchange fluid 85 between the inner and outer tubes 190 and 192at the distal end 45.

This loss of the heat exchange fluid 85 can also be addressed with aseal tube 234 which can be positioned between the inner and outer tubes190, 192 and inwardly of the hollow fibers 198. In this embodiment, adistal end 236 of the seal tube 234 is generally coextensive with thedistal end of the outer tube 192. The seal tube 234 is preferablyprovided with an inner diameter greater than the outer diameter of theinner tube 190. As a result, the inner tube 190 is free to move relativeto the outer tube 192 to achieve the advantages previously discussed.However, when the inner tube 190 is drawn sufficiently proximal of theouter tube 192, the taper 232 will contact the distal end 236 of theseal tube 234. This effectively forms the seal between the inner andouter tubes 190 and 192, respectively at the distal end of the outertube 192. With the taper 232 wedged against the seal tube 234, thefibers 198 are maintained in their operative free-floating configurationas illustrated in FIG. 24.

Alternatively, a non-tapered inner tube 190, can be mated with a closelyfitted seal tube 234. With very small and controlled differences betweenthe outside diameter of the inner tube 190 and the inside diameter ofthe seal tube 234, for example 0.0005 to 0.003 inches, an effective sealcan be constructed without the taper 232. This embodiment relies on thelength of the seal tube 234, the surface tension of the coolant fluid85, and the small capillary gap to create a resistance greater than thepressure of the coolant fluid during operation. This design does notrequire the inner tube to be moved a fixed distance relative to theouter tube and does not require a constant tension between the inner andouter tubes to effect a seal.

The seal tube 234 is preferably constructed of polyimide which allowsfor a precision and constant inner diameter. In addition, polyimide isavailable in very thin wall thicknesses so that the seal tube 234 willnot occupy a significant portion of the annular space which is moreappropriately dedicated to the fibers 198.

A method for manufacturing the hollow fiber embodiments of the catheter10 is illustrated in FIGS. 25-27. In FIG. 25, a planar mat 241 of thehollow fibers 198 is formed with a generally planar configuration. Inthis mat 241, the fibers 198 are oriented in a generally parallelconfiguration with angled potting seals 201 and 243 formed at oppositeends of the fibers 198. This fiber mat 241 can be rolled onto the outersurfaces of the inner tube 190 and seal tube 234 as illustrated in FIG.26. In this step, the potting seal 201 is formed around the distal endof the inner tube 190 while the potting seal 243 is formed around thedistal end of the seal tube 234.

By initially forming the fibers 198 into the mat 241, a generallyuniform thickness of the mat 241 can be maintained. Rolling the mat 241onto the tubes 190 and 234 maintains this uniform thickness and alsofacilitates orientation of the fibers 198 onto the cylindrical tubes 190and 234. This technique also forms an inwardly spiraling helical bondjoint profile that aids in directing the blood flow in order to inhibitclot formation by preventing stagnant blood flow areas at the bondjoint. With the potting seals 201 and 243 suitably bonded to the tubes190 and 234, respectively, the cap 205 can be mounted over the distalend of the fibers 198 as previously discussed. At the proximal end ofthe fibers 198, the seal tube 234 can be mounted in the distal end ofthe outer tube 192 as illustrated in FIG. 27.

The seal tube 234 offers some interesting possibilities for the infusionof fluids at the distal end 45 of the catheter 10. Of course, it isalways possible to provide an additional lumen within the shaft of thecatheter 10. In such an embodiment, the fluid to be infused could beinjected into the additional lumen at the proximal end 43 to exit thecatheter at the distal end 45. Alternatively, the fluid to be infusedmight be included in the heat exchange fluid 85. The tolerance betweenthe seal tube 234 and the outer diameter of the inner tube 190 couldthen be controlled to provide a calibrated leak of the heat exchangefluid 85 at the distal end 45 of the catheter 10. Micro holes might alsobe drilled into the outer tube 192 or inner tube 190 to provide for acontrolled leakage of the infusion fluid.

Each of the foregoing embodiments of the heat exchange catheter 10 isadapted for use in cooling the entire human body, or perhaps only aportion of the total body. Methods of operation will vary widelydepending on the focus of a particular procedure. By way of example, itwill be noted with reference to FIG. 28 that the catheter 10 isparticularly adapted for cooling blood in a procedure which may involveas many as three of the catheters 10. In FIG. 28, a human body 245 isillustrated along with a portion of the blood circulatory systemincluding a pair of femoral veins 247, 250 and a subclavian vein 252.These veins 247, 250 and 252 all extend into the vena cava 254 of thebody 245. In this procedure, separate catheters, such as the heatexchange catheter 10, can be introduced into each of the femoral veins247, 250 and the subclavian vein 252 with their respective heat exchangeregions disposed in the vena cava 254. Alternatively, and preferably,only two such catheters would be introduced from two of the three veins247, 250 and 252.

A systemic version of the catheter might have a diameter in a range ofbetween 9 and 15 French, and a length of approximately 20 to 80centimeters long. It is contemplated that this design could conceivablycool the body in several hours. The use of two such catheters insertedinto the vena cava 254 as mentioned above could be expected to reducethe time required to cool the body by a factor of 2. It will beappreciated that similar catheters and methods can be used to lower thetemperature of blood in the native carotid or in the vertebralcirculatory system. The amount of blood heat lost is directlyproportional to the temperature differential, the blood velocity and theblood-to-catheter surface area.

Particularly in an operative setting wherein the heat exchange catheter10 is to be inserted into a blood vessel, a further design feature bestillustrated in FIGS. 29-33 will be of particular interest. In theseviews, an introducer 256 is positioned for percutaneous insertion into ablood vessel such as the femoral vein 250. A sleeve 258 is provided onthe catheter 10 and slidable along the outer tube 192 between twopositions. The first position is illustrated in FIG. 29 wherein thesleeve 258 is disposed in a spaced relationship with the heat exchangeregion 47. The second position of the sleeve 258 is illustrated in FIG.30 where the sleeve 258 covers the heat exchange region 47. In thisposition the balloons or fibers associated with the region 47 arecompressed to a low profile state greatly facilitating introduction ofthe catheter 10 into the introducer 256. In addition, the covered heatexchange region 47 is stiffened for easier introduction into theintroducer 256. The fibers and/or balloons are also protected from theinterior surface of the introducer 256. Optionally, a stiffening mandrilmay be inserted down one or more of the tubes 190, 192 to facilitateintroduction of the catheter 10 into the introducer 256.

After this initial insertion, the sleeve 258 remains within theintroducer 256 while the remainder of the heat exchange region 47 ismoved distally into the conduit as illustrated in FIG. 31. At thispoint, the sleeve 258 can be removed from the introducer 256 by slidingit proximally to its first position as illustrated in FIG. 33.

This method of introduction is facilitated by providing the sleeve 258with a generally cylindrical configuration. The diameter of thecylindrical sheath should be less that the inside diameter of theintroducer 256. However, at the proximal end of the sheath 258, anannular flange 261 or other enlargement can be provided to ensure thatthe sheath 258 does not pass beyond the introducer 256.

Another feature associated with the present invention relates to a bloodclot basket or snare 263, best illustrated in FIGS. 34 and 35. Thissnare 263 is preferably positioned downstream of the heat exchangeregion 47 associated with the catheter 10. It being appreciated that anystructure disposed in a blood vessel may tend to generate blood clots,it is the purpose of the snare 263 to capture any such clots. The snare263 of the preferred embodiment includes a plurality of wires 265 whichextend along a shaft 267 with their opposing ends fixed in the manifold194 and a distal cap 270. The wires 265 in a preferred embodiment areformed of stainless steel or a nickel titanium alloy.

In the illustrated embodiment, the shaft 267 extends to the proximal end43 of the catheter 10 either through the lumen of the inner tube 190 oralternatively through a second, separate lumen in the inner tube 190. Inthe former case, a seal would be required at the distal end of themanifold 194 to prevent any leakage of heat exchange fluid 85 around theshaft 267.

In either case, the shaft 267 is free to move relative to the concentrictubes 190 and 192. When the shaft 267 is moved relatively distally, thesnare wires 265 are provided with a generally low profile. When theshaft 267 is moved relatively proximally, the wires 265 deploy toprovide the snare with an enlarged high-profile configuration asillustrated in FIG. 35.

In a further embodiment of the snare 263, the wires 265 are connected tothe manifold 194 and extend to distal ends which are unattached or free.The wires 265 in this embodiment, best illustrated in FIG. 36, are bentto a deployed enlarged configuration. With such an embodiment, insertionis facilitated by providing a delivery sheath which is movable tomaintain the wires 265 in a low-profile state. Once the catheter 10 isin place, the sheath 262 can be removed thereby permitting the wires 265to automatically expand to their enlarged high-profile state.

With respect to the forgoing disclosure as a whole, it will be apparentthat many variations from these preferred embodiments will now beapparent to those skilled in the art. For example, with respect to theballoon embodiments previously discussed, it will be appreciated thatthe advantages of this invention can be derived with only a singleballoon. On the other hand, there seem to be several advantagesassociated with multiple balloon embodiments. Notably, a more even andbalanced transfer of heat exchange can be achieved with multipleballoons. In addition, there appears to be better mixing with respect toboth the blood 31 as well as the heat exchange fluid 85. Multipleballoons also provide an increased surface area relative to singleballoon embodiments. Furthermore, the overall flexibility of thecatheter 10 is enhanced with multiple balloons separated byinterruptions which provide natural flex points for the catheter. Whenthe balloons experience the high perfusion pressure, they become morestiff. The reduced diameter interruptions provide for increasedflexibility at these joints.

Additional flexibility can be derived by providing the shaft 40 withvariable stiffness. This variability can be produced by differentmaterials forming the shaft 40 along its length or alteratively,tapering or otherwise varying the diameter of the shaft 40. For example,the shaft 40 can be progressively tapered from its proximal end 43 toits distal end 45 in order to provide a softer and more flexible heatexchange region 47.

In any of the foregoing embodiments of the catheter 10, the inner tube190 can be provided with a central lumen facilitating introduction overa guidewire and providing a capability for the infusion of fluidsthrough the catheter 10.

With the intent of maximizing heat transfer with the body fluid in aconduit feeding a specific region of the body, any of the factorspreviously noted can be addressed to provide structural modifications tothe foregoing embodiments. Of course changes in the material or size ofany of the structural elements described can be varied to achievevarious heat exchange properties. Realizing the many changes which mightbe contemplated, one is cautioned not to limit this concept only to thespecific embodiments illustrated and disclosed, but rather to determinethe scope of the invention with reference to the following claims.

What is claimed is:
 1. A catheter having an elongate configuration witha proximal end and a distal end, the catheter comprising: an outer tubehaving an elongate configuration and a first lumen; an inner tubedisposed in the first lumen of the outer tube and having a second lumenextending between the proximal end and the distal end of the catheter;portions of the inner rube defining a first fluid flow path extendingalong the second lumen between the proximal end and the distal end ofthe catheter; portions of the outer tube and the inner tube defining asecond flow path extending between the first tube and the second tube; aplurality of hollow fibers providing fluid communication between thefirst fluid flow path and the second fluid flow path; each of the hollowfibers has a proximal end and a distal end; the distal end of each ofthe hollow fibers has a fixed relationship with the distal end of theinner tube; the inner rube has properties for moving relative to theouter tube to vary the configuration of the hollow fibers extendingbetween the inner tube and the outer tube; the proximal end of each ofthe hollow fibers has a fixed relationship with the distal end of theouter tube; a seal tube disposed between the hollow fibers and the innertube and having an inner diameter greater than the outer diameter of theinner tube, but sufficiently close to the outer diameter of the innertube to form a liquid seal between the seal tube and the inner tube bycapillary action; and portions of the inner tube define a taper, theinner tube being axially movable to bring portions of the inner tubeinto sealing proximity with the distal end of the seal tube.
 2. Acatheter having an elongate configuration with a proximal end and adistal end, the catheter comprising: an outer tube having an elongateconfiguration and a first lumen; an inner tube disposed in the firstlumen of the outer tube and having a second lumen extending between theproximal end and the distal end of the catheter; portions of the innertube defining a first fluid flow path extending along the second lumenbetween the proximal end and the distal end of the catheter; portions ofthe outer tube and the inner tube defining a second flow path extendingbetween the first tube and the second tube; a plurality of hollow fibersproviding fluid communication between the first fluid flow path and thesecond fluid flow path, liquid flowing through the fibers; a capdisposed over the distal ends of the inner tube and the hollow fibers;and a coating of insulation covering the cap at the distal end of thecatheter.